The DI can is formed by punching the metal plate into a circular blank, forming the blank into a cup through the drawing with one or more stages, further forming the cup into a redrawn cup through the drawing with one or more stages, and passing an ironing die with one or more stages so as to reduce a thickness of a side wall of the redrawn cup. The aforementioned series of the process will be referred to as a DI process.
Recently the metal plate coated with the resin film such as the one capable of omitting the coating step has been attempted to be applied to the DI process in view of the environmental preservation. In the case where the metal plate coated with the organic resin (or the organic resin coated metal plate) is subjected to the DI process, the resin film is likely to fall off as a hair-like peeling at the opening end of the body of the can, which is so called a hair. The hair tends to adhere to the blade for the blank punching, the punch or die for the drawing or ironing, and the portion around the area of the can manufacturing apparatus where the series of the process steps are performed, and to be accumulated thereon. The aforementioned adhesion and accumulation may cause the working defect such as the breakage of the body of the can and the mark on the can surface. The hair which is kept adhered to the body of the can deteriorates the outer appearance thereof, and triggers the working defect in such process as necking and flanging to be performed after the drawing and the ironing. The hair causes the serious problem when performing the DI processing of the organic resin coated metal plate.
Several types of the arts for coping with the problem of the hair have been disclosed.
Patent Document 1 discloses the art for avoiding generation of hair. Upon the blank punching for manufacturing a drawn can and a drawn-squeezed can made of a resin coated metal plate, stage differentials are made on edges of the blanking punch and the blanking die. The blank is punched to have the resin film on the blank edge slightly smaller than the metal plate as base, and the blank is subjected to the drawing and squeezing to form the drawn can and the drawn-squeezed can.
Patent Document 2 discloses the art for preventing generation of hair by widening the interval between the annular holding member (wrinkle suppression) and the die at the point of the effective drawing stroke length from 65 to 98% to be larger than the thickness of the work for the purpose of rendering the roll-separating force of the flange just before the end of the drawing process as the cause of the hair generation harmless, and releasing the rear end of the flange part to be drawn in.
Patent Document 3 discloses the art of drawing-ironing of the metal plate having the single surface or both surfaces coated with the organic resin, which includes the step of forming the region at the outer edge of the organic resin coated metal plate having the thickness gradually decreased toward the outermost circumferential part before performing the drawing. The aforementioned step allows the thickness of the outermost circumferential part of the organic resin coated metal plate to be smaller than the maximum thickness of the side wall of the ironed organic resin coated metal plate to prevent the resin film at the opening end of the can body from peeling off as the hair by the ironing die.
Patent Document 4 discloses the art for preventing generation of hair, which includes the steps of preliminarily coating the thermoplastic resin over the face to be made as the internal side of the can of the metal sheet, subjecting the resin coated metal plate to the drawing to form the cup, heating the peripheral circumference of the cup to subject the thermoplastic resin chip which extends to the outside from the upper end of the cup generated through the drawing to the heat shrinkage to form the exposed metal surface which contains no thermoplastic resin on the cup opening, and performing the redrawing, or redrawing-ironing process after fusing the heat shrunk resin.
Patent Document 5 discloses the art for preventing generation of hair upon manufacturing of the metal container through the cup-forming or draw-ironing forming by using the metallic sheet having at least the single surface coated with the resin film by performing laser irradiation before or after the cup-forming to remove a part of the surface-coated resin layer.
The aforementioned disclosed arts are based on the concept for preventing generation of the hair by the can manufacturing process. Meanwhile, the art for avoiding generation of the hair by controlling the metal plate property has also been disclosed.
Patent Document 6 discloses the art for avoiding generation of hair when forming the drawn-ironed can from the resin coated metal plate by adjusting the steel content and material of the steel plate as the base, further adjusting the surface strength ratio of the crystal surface to allow the use of the steel plate which is thinner than the generally employed material, reducing the substantial ironing quantity in the ironing step at which the hair is mostly generated, and suppressing the working hardening during the process to prevent increase in the deformation resistance.
Patent Document 7 discloses the art for avoiding generation of hair when subjecting the organic resin film coated steel plate to the DI forming by adjusting the steel content of the steel plate as the base and the manufacturing method for softening the strength and controlling the crystal grain size.
Patent Document 7 discloses the art for removing the adhered substance generated in the DI forming process rather than the hair. In the method for processing the drawn-ironed can for manufacturing the processed can body which employs the die with the through hole and the punch that can be inserted into the through hole having the small gap left therebetween, the work is pressed and passed through the through hole by the punch under the dry environment, and the wiping means on the punch serves to remove the substance adhered to the inner circumferential portion. The aforementioned art is based on the concept for removing the adhered substance rather than the concept for preventing generation of the adhered substance.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-94121
Patent Document 2: Japanese Unexamined Patent Application Publication No. 5-154570
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2004-344940
Patent Document 4: Japanese Unexamined Patent Application Publication No. 9-19733
Patent Document 5: Japanese Unexamined Patent Application Publication No. 2005-296998
Patent Document 6: Japanese Unexamined Patent Application Publication No. 2003-277885
Patent Document 7: Japanese Unexamined Patent Application Publication No. 2004-255452
A flangeless cup may be obtained through the drawing while suppressing generation of the hair. However, it is impossible to suppress generation of the hair upon the ironing for reducing the thickness of the wall of the can using the ironing die with multiple stages after the drawing. In the ironing, high pressure is exerted to the drawn flangeless cup by the multi-stage ironing die to reduce the thickness of the wall of the can. As a result, the high pressure is unavoidably exerted to the cup edge, which is likely to generate the hair. The aforementioned problem occurs in spite of the use of the art as disclosed in Patent Documents 1 to 7.
Generation of the hair may need the step of removing/collecting the hair from the can manufacturing apparatus, and the step of removing the hair adhered to the drawn-ironed can after processing. This may considerably deteriorate productivity of the drawn-ironed can.
The present invention provides an ironing method and an ironing apparatus which allow removal of the adhered substance such as the hair.